For example, in an internal combustion engine used as a power source of an automobile, a fuel injection valve injects fuel and the fuel is ignited in the combustion chamber of a predetermined cylinder. The fuel is burned, thereby producing torque to rotate a crankshaft as an output shaft. In recent years, a multi-stage injection is employed in a diesel engine for an automobile. In the multi-stage injection, a small amount of injection as sub-injection is performed before or subsequent to the main injection in one burning cycle. In recent years, noise at the time of combustion and increase in NOx exhaust cause a problem. Therefore, for enhancing combustion, a pilot injection and a pre-injection may be performed with a little injection quantity before a main injection. After the main injection, an after-injection may be performed for diffusing combustion, reduction in particulate matter discharge, and the like. An injection timing of the after-injection is close to the main injection in the combustion. Alternatively, a post-injection may be performed for increase in temperature of exhaust gas, activation of a catalyst by supplying an oxidization component, and the like. The injection timing of the post-injection is at a timing greatly retarded. With respect to the main injection after the end of combustion. In recent years, fuel supply to the engine is performed by one or combination of the various kinds of injection in an engine control. The present engine control produces an injection mode (injection pattern), which is more suitable to various situations.
In the multi-stage injection, various kinds of control devices are employed for determining an injection pattern according to an engine operation state in each time by using a data map or an equation. A conformed value corresponding to the injection pattern for each engine operation state is written in the data map or the equation. The present control device stores the conformed value, which is determined beforehand correspondingly to each engine operation state, as a data map, equation, and the like in a ROM. The conformed value for each engine operation state is an optimal pattern, which is determined beforehand by an experiment or the like for each engine operation state, which is beforehand assumed. The present control device determines the injection pattern according to the engine operation state with reference to the data map, the equation, and the like. A device described to JP-A 2005-264810 switches an injection pattern according to engine operation conditions. Thus, the device is capable of supplying fuel to an engine also in multi-stage injection, by using the data map and the equation defining the conformed value therein, at an injection mode suitable for the engine operation state in each time. However, when multi-stage injection is performed using such a device, injection is continuously performed at a short interval. The inventor found that a control error with respect to a target engine operation state becomes larger in the multi-stage injection, compared with the case of the single-stage injection. For example, a small amount of continuous sub-injections may receive various influences by injections in advance of and subsequent to the sub-injection. The influence relates to an injection characteristic associated with, in particular, an individual difference among injectors as fuel injection valves.
For example, when each element of an engine control system is mass-produced, such individual difference usually arises in the characteristic of various kinds of control components. Specifically, individual difference in the characteristic of various kinds of control components including the fuel injection valve also arises between engines or between cylinders of a multi-cylinder engine. However, in a mass-production, it is difficult to obtain the conformed value and the optimal injection pattern in view of individual differences for all the control components and all the cylinders. Therefore, even when the data map and the equation, in which the conformed value was written, are used, it is difficult to perform the fuel injection control in consideration of all the influences caused by the individual difference. In addition, the inventor further found that the injection characteristic related to the multi-stage injection is also influenced by the individual difference, in performing the multi-stage injection. That is, unlike the case of the single-stage injection, an influence is further caused among multiple injections in the multi-stage injection. Therefore, it is also necessary to consider the injection characteristic of multi-stage injection in order to obtain an engine operation state at high accuracy in multi-stage injection, in addition to the injection characteristic of single-stage injection. Accordingly, in a case where the conventional device described in JP-A 2005-264810 is applied to control the multi-stage injection, it becomes difficult to control the engine operation state at high accuracy.
Furthermore, a characteristic change resulting from aging in control components, and the like is not negligible for performing the injection control at high accuracy. In the conventional device described in JP-A 2005-264810, the optimal value may be obtained at high accuracy in an initial condition. However, the optimal value cannot be obtained due to the influence caused by a subsequent characteristic change. Accordingly, it is apprehended that a deviation from the optimal value may progress as time passes. It is also considered that a conformed value defining a coefficient may be beforehand determined in accordance with a degree of aging degradation obtained by an experiment, and the conformed value may be defined as a data map, equation, and the like. However, each component also has such an individual difference in aging characteristic change. Therefore, it is difficult to eliminate the influence caused by the individual difference.